The invention is related to an apparatus and method for making tubes for a heat exchanger and in particular to tubes having a convoluted fin insert in which the convolutions are transverse to the length of the tube.
The use of cooling tubes in heat exchangers having rectangular or oblong cross-sections such as taught by Wallis in U.S. Pat. Nos. 4,595,135 and 4,971,240 are well known in the art. More recently, Wallis in U.S. Pat. No. 5,271,151 discloses the formation of a plurality of parallel longitudinal flow paths within an oblong cooling tube. Alternatively, Dudley in U.S. Pat. No. 5,372,188 and Guntly in U.S. Pat. No. 4,998,580 disclose the use of inserts convoluted in a direction parallel to the length of the cooling tube to form the plurality of parallel longitudinal fluid flow paths called turbulators within the cooling tubes, while Study in U.S. Pat. No. 5,456,006 describes a method for inserting a turbulator into the cooling tube during the formation of the cooling tube. In the above cooling tubes the turbulators form small longitudinal flow paths extending parallel to the length of the cooling tube. This configuration is well adapted to charge air coolers.
In an alternate configuration of the cooling tube, Bae in U.S. Pat. No. 5,771,964 teaches a cooling tube in which small fluid flow channels are provided transverse to the length of the cooling tube. This type of geometry produces a more efficient heat exchanger.
Against this background, the need has arisen for cost-effective manufacture of extruded tubes used in heat exchanging, i.e., condensing, applications. One requirement for instance, of refrigeration condensers is to supply the largest surface area to the compressed gases and be able to contain high internal (and often varying) pressures without distortion or leak.
The invention is an apparatus and method for inserting a high-density insert such as a fin, into a tube having an oblong cross-section as the tube is being formed. The high-density insert in cooperation with the internal surfaces of the tube forms a plurality of transverse fluid paths.
The disclosed invention includes the utilization of a high density insert, having convolution counts well above the normal thirty convolutions per inch. Such an insert provides enhanced surfaces required for superior heat transfer characteristics. The disclosed insert is bonded to the inside of a heat transfer tube, wherein it offers a long, tortuous path which is conducive to efficiency of heat transfer. The enhanced insert may or may not have any louvers, as is customary in air side fins conventionally manufactured.
The disclosed structure provides a high internal strength which retains high pressure. Strength is provided by bonding the insert to the interior surface of flattened oval tubes. The disclosed sinusoidal insert supports internal forces that define a truss-type form, thereby presenting a stiff construction. If brazed, the form of the convolutions after they are compressed, defines cavities which a molten clad fills, thereby forming a fillet bond.
An apparatus and for making a tube for a heat exchanger includes a first set of rollers to form a continuous longitudinal shell from a metal strip, and inserting a continuous insert into the shell as the shell becomes closed. The insert has high density convolutes transverse to the length of the continuous shell. Optionally, the insert is supported within the shell by a series of dimples. The continuous shell with the insert is closed, and then bonded to seal the open edges of the strip to each other as it passes through a bonding device (preferably an induction heater). The method concludes with the slicing the sealed continuous tube into individual segments to produce desired lengths of cooling tubes.
An object of the invention is to make a tube for a heat exchanger including an insert having high density of convolutions transverse to its length.
Another object of the invention is the addition of dimples in the outer shell to locate (preferably centrally) and support the insert inside the finished tube.
Still another object of the invention is to provide detents in the outer shell from blocking the fluid channels formed in the sealed shell on opposite sides of the insert to form a serpentine fluid path through the cooling tube.
Another object of the invention is a method for making a tube in which the insert is loaded into the shell as the tube is being formed.
Still another object is to provide a cooling tube having superior heat transfer properties.
Yet another object is to manufacture a cooling tube with a high density convoluted insert having convolutes transverse to the length of the tube.
A further advantage of the invention is that it is a cost efficient way to fabricate uniform cooling tubes for heat exchangers having an internal insert.
These and other advantages of the invention will become more apparent from a reading of the Specification in conjunction with the drawings.